The present invention relates to novel kinesin polypeptides, polynucleotides encoding same, pharmaceutical compositions and uses thereof.
Kinesins are motor proteins that play a role in intracellular positioning and trafficking of intracellular components, mRNA and protein. These cytoskeleton-dependent motor proteins have been implicated in both gene expression and cell differentiation. Their associated molecular motor action is based on hydrolysis of ATP to produce force and movement along microtubules.
Structurally, kinesins consist of three functional parts: a motor domain that reversibly binds microtubules and converts chemical energy into the motion; a central helical coiled coil domain, which possesses protein-protein interactions; and a tail, which interacts with cargo and regulates the motor activity. The motor domain comprises a signature of 340 amino acid residues that transduces ATP hydrolysis into directed movement along a microtubule. The specificity of the interaction of kinesins with their cargo is determined by their tail domains, which are divergent from one another. Although more than 50 kinesin proteins have been identified only a few of their specific cargos are known. For example, KIF13A binds cargo vesicles of AP-1 and mannose-6-phosphate receptor (M6PR). KIF17 was shown to interact with the PDZ domain of sorting protein mLin-10 (Mint1/X11), which is a component of a large complex that includes mLin-2 (CASK), mLin-7 MALS/Velis and the transmembrane protein NR2B, a subunit of the N-methyl-D-aspartate (NMDA) receptor.
Estrogens are an important class of steroidal hormones that stimulate the development and maintenance of fundamental sexual characteristics in humans. In addition, estrogens have been demonstrated to affect a variety of diverse biological processes. Many of the incidental effects of estrogens are positive, including the maintenance of bone density, central nervous system function and preservation of memory. However, estrogens also have been demonstrated to have serious negative effects, including promoting the development of breast and endometrial cancers.
The estrogen effect on cellular metabolism is mediated by two receptors—ERα and ERβ which belong to the steroid nuclear receptor superfamily. The receptor consists of several domains. The A/B domain at the N-terminus encodes the ligand-independent activation function domain (AF1). This is responsible for protein-protein interactions. The DNA-binding domain (DBD) mediates receptor binding to promoters of estrogen-regulated genes. Region D is a flexible hinge region between DNA and the ligand-binding domains (LBD). The C-terminal consists of the AF-2 domain, which is involved in interactions with transcriptional co-activators via nuclear receptor boxes comprising LXXLL-motifs.
ERα is expressed by two splice forms; the 66 kDa and the 46 kDa, which lacks the AF-1 domain. The estrogen receptor binds its ligand in the cytoplasm and is then translocated to the nucleus. The receptor binds to genes comprising estrogen response elements (ERE) or to transcription factors such as AP-1 and SP1 thereby regulating other genes.
The nuclear signaling of estrogen occurs within 30-60 minutes following hormonal treatment. An alternative rapid (seconds to minutes) pathway is activation of Mitogen Activated Protein Kinases (MAPKs) such as p38 and ERK1/2. This leads to an increase in cAMP or Inositol 1,4,5-trisphosphate (IP3), both of which are mediators of the non-genomic actions of estrogen.
The estrogen receptor (ER) is localized to different cellular compartments, including the cell membrane, cytoplasm, and nucleus and it is known to shuttle dynamically in the cell. Various mechanisms have been proposed to explain how proteins in general and receptors specifically translocate in a cell. In this regard it has been suggested that kinesin may play a role in intracellular protein shuttling. As yet, no kinesin has been shown to bind to the estrogen receptor.
Due to estrogen's far-reaching effects, there is a widely recognized need for, and it would be highly advantageous to have, novel estrogen receptor modulators.